Drew,
I am not sure what exercise you are referring to, more explanation may be required, such as what position you are doing them in, and what body part you are extending. Extending your shoulder in standing would be to move your arm back behind you, which would generally cause more pain with a rotator cuff injury.
Hierovision,
I am assuming you did not have a rotator cuff repair, and had something more simple like an acromioplasty. I would not allow any of my patients to play pool after 6 wks post op RTC repair if it was their bridge arm. An acromioplasty or something similar could be a different story.
Leehayes,
I would think the trouble you are having with your accuracy would be stemming more from your bridge arm than your back arm (not that it could not be your back arm), especially if the back arm does not hurt during your stroke. When you put your arm into the bridge position, it can impinge the rotator cuff between the humeral head (your upper arm bone) and a bone from your shoulder blade called the acromion. The supraspinatus muscle, the most commonly torn RTC muscle runs in between them. This is a fairly common problem in pool players. My first suggestion would be to bend your elbow. This will decrease the angle at your shoulder. You really want it be under 90 degrees of elevation if possible, with under 60 being the best. 60 would be almost impossible to shoot pool with though. The less angle at you shouilder though, the less change for the impingement. The other things that may help are icing the shoulder (or heating) to decrease inflammation, and possibly strengthening the 3 other muscles of the RTC to help them perform their function. You may have to be careful with these though depending on how much you other muscle is torn. In general, getting a decent ex program from a physical therapist will be your best initial treatment, with surgery possibly being your only permanent solution depending on the size of your tears. PM with anymore questions, or if you would like more detailed info. I work with these types of injuries all the time.